Metal golf club head

ABSTRACT

A metal golf club head includes: a metal head main body; and an anticorrosion screw that is formed from a magnesium alloy and fastened to predetermined location on the metal head main body.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a metal golf club head which generates superior feeling of hitting and a superior hitting sound.

2. Description of the Related Art

A metal golf club head having a hollow section has become larger in size. Of so-called drivers head having a loft angle of 13° or less, a driver head having a head volume of 300 cc or more, particularly 350 cc to 500 cc, has come predominant. In the case of the driver head, a head weight is 200 g or less and preferably ranges from 180 g to 195 g or thereabouts; and the specific gravity of a titanium alloy ranges from 4.2 to 5.0. Hence, a crown, sides, and a sole are made smaller in thickness. In some cases, partially reducing the thickness of a face has hitherto been performed.

In a heretofore driver head which is formed from a titanium alloy (e.g., Ti-6Al-4V) through casting and has a hollow section, each of a crown, a sole, and sides has a thickness of about 1.2 mm, and a face has a thickness of about 3 mm. Recently, portions (a sole, sides, a crown, a face, or a part formed integrally from two or more of these portions) of a golf club head are formed by means of pressing a plate material, such as a β-type titanium alloy, and the like; and these portions are welded together, to thus manufacture a golf club head having a hollow section, as disclosed in JP-A-2003-52866. In relation to casting, there has been adopted a method for melting metal by means of a lost wax method (an investment casting method) and pouring the melt metal into a ceramic mold. Difficulty is encountered in reducing the thicknesses of respective portions. A method for forming respective portions of a golf club head by means of pressing enables a reduction in the thicknesses of the respective portions. Hence, a thickness of 1 mm or less becomes feasible, which has enabled manufacture of a larger golf club head.

SUMMARY OF THE INVENTION

However, as a result of a reduction in the thickness and an increase in the size of the golf club head, vibrations developing in the golf club head when the club head hits a golf ball become greater, which unpreferably affects the feeling of hitting and hitting sound.

The present invention is conceived in view of the circumstances and aims at providing a metal golf club head which generates enhanced feeling of hitting and hitting sound.

In order to achieve the object, the present invention provides a metal golf club head including: a metal head main body; and an anticorrosion screw that is formed from a magnesium alloy and fastened to predetermined location on the metal head main body.

The meal golf club head of the present invention effectively dampens vibrations of the golf club head resulting from hitting of a golf ball by means of the anticorrosion screws of a magnesium alloy, and feeling of hitting and hitting sound are enhanced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective view showing a head main body of a metal golf club head of an embodiment of the present invention, and FIG. 1B is a cross-sectional view of the head main body taken along T1-T1 shown in FIG. 1A;

FIG. 2A is a perspective view of the head main body when viewed from a direction differing from that where FIG. 1A is acquired, and FIG. 2B is a cross-sectional view of the head main body taken along T2-T2 shown in FIG. 2A;

FIG. 3 is an enlarged cross-sectional view showing that screws formed from a magnesium alloy are mounted to the head main body; and

FIG. 4 is a graph showing a relationship between vibration frequencies and damping ratios of golf club heads of an embodiment and comparative examples.

DETAILED DESCRIPTION OF THE EMBODIMENTS

An exemplary embodiment of the present invention will be described in detail below. In the exemplary embodiment, no limitations are imposed on the material of a metal head main body. However, for example, a titanium alloy, stainless steel, an aluminum alloy, low carbon steel (e.g. S15C or S25C), and the like, are mentioned. The metal head main body may also be realized by an article integrally formed by means of casting or connecting a plurality of parts through welding or the like.

No limitations are imposed on the type of a metal head main body employed in the exemplary embodiment. A light-weight driver head having a small thickness is particularly preferable. For instance, a driver head—which is formed from, e.g., a titanium alloy (of, e.g., a specific gravity of about 4.5) or an aluminum alloy (of, e.g., a specific gravity of about 2.7) and has a head volume of 300 to 500 cc—can be preferably used. In the case of a head formed from stainless steel having large specific gravity (for example, a specific gravity of 7.8), a driver head having a head volume of 200 to 300 cc can be used preferably. In relation to the thickness of the head, the least thickness of the crown, the sole, and the sides is appropriately set to 0.5 mm to 1.0 mm, particularly 0.6 mm to 0.9 mm. Moreover, the metal head main body employed in the exemplary embodiment is not limited to a hollow golf club head but may also be a solid golf club head such as an iron club head.

In the exemplary embodiment, the type of the magnesium alloy is not limited. An alloy made by adding aluminum and zinc to magnesium can be preferably used. More specifically, an AZ31 alloy made by adding 3 percent by mass aluminum and 1 percent by mass zinc to magnesium, an AZ61 alloy made by adding 6 percent by mass aluminum and 1 percent by mass zinc to magnesium, an AZ91 alloy made by adding 9 percent by mass aluminum and 1 percent by mass zinc to magnesium, and the like, can be used preferably. However, the magnesium alloy is not limited to them.

The weight of one screw which is used in the present embodiment and formed from a magnesium alloy preferably ranges from 1 to 5 grams. When the screws are too light in weight, an effect of damping vibrations of the head is not achieved. In contrast, when the screws are too heavy in weight of a head is affected undesirably. The specific gravity of the magnesium alloy is of the order of 1.7 to 2.0 or thereabouts. The Young's modulus of the magnesium alloy is 44 to 45 Gpa which is one-half or less the Young's modulus of the titanium alloy or about 60 to 70 percents of the Young's modulus of the aluminum alloy.

Since the magnesium alloy is susceptible to corrosion, the surfaces of the screws are subjected to corrosion treatment. Specifically, the surfaces of the screws can be subjected to corrosion treatment by means of chromate (hexavalent chromium) treatment, permanganate treatment, anodizing, zinc phosphate, and the like, or the surfaces of the screws can be subjected to corrosion treatment by means of coating the surfaces with insulating coating or an insulation resin. In the exemplary embodiment, corrosion treatment is assumed to include rustproofing.

Particularly-preferred corrosion treatment is to form an oxide film on the surfaces of the screws by use of anodizing. Moreover, the magnesium alloy is likely to cause electrolytic etching upon contact with metal of different type. Hence, at least external threads of the screws formed from a magnesium alloy are preferably coated. Moreover, female screws of the head main body which contact the screws formed from a magnesium alloy are preferably coated. It is appropriate to use, for coating application, epoxy-based coating exhibiting superior adhesion to a magnesium alloy coated with an oxide film.

In the exemplary embodiment, screws formed from a magnesium alloy can be manufactured, by means of machining, from a round bar consisting of a magnesium alloy. Since the magnesium alloy is lower than an aluminum alloy or stainless steel in terms of cutting resistance, the magnesium alloy is easily machined. Screws formed from a magnesium alloy are manufactured by means of machining. After soil on the surfaces of the screws is eliminated by alkaline cleansing, the screws can be subjected to acid cleansing for the purpose of corrosion treatment.

In the exemplary embodiment, an adhesive can be applied to external threads of the screws formed from a magnesium alloy or female screws of the head main body with which the external threads of the screws formed from a magnesium alloy are to be screw-engaged. As a result, removal of the screws formed from a magnesium alloy from the head main body can be prevented effectively. For instance, an epoxy-based adhesive can also be used as an adhesive. In the exemplary embodiment, adhesion between the screws and the head main body can be enhanced by means of subjecting the screws formed from a magnesium alloy to corrosion treatment.

In the exemplary embodiment, after the screws formed from a magnesium alloy are fastened to the head main body, the surfaces of the head main body can be coated. By means of coating, clearance between the head main body and the screws formed from a magnesium alloy is covered with the coating film, and hence intrusion of dust or moisture into the clearance can be prevented. Moreover, an anaerobic adhesive exhibiting superior permeability, such as an acrylic adhesive or the like, may also be poured into the clearance between the head main body and the screws formed from a magnesium alloy. Since the anaerobic adhesive becomes cured after having entered clearance between the head main body and the screws formed from a magnesium alloy, there can be yielded an advantage of the ability to prevent loosening of the screws or intrusion of dust or moisture components into the clearance.

In the exemplary embodiment, it is preferable to attach screws formed from a magnesium alloy to sides of the metal head main body; particularly recesses of the sides of the metal head main body, such that the screws formed from a magnesium alloy do not protrude into the recesses. When the screws formed from a magnesium alloy are attached to the sole, the sole contacts a ground during the course of swinging action. Hence, it may be the case where flaws arise in the screws formed from a magnesium alloy, to thus exfoliate the oxide film or paint, and where the flows give rise to corrosion of the screws formed from a magnesium alloy. However, when the screws formed from a magnesium alloy are attached to the sides, such inconvenience does not arise. Further, as a result of the screws formed from a magnesium alloy being attached to recesses formed in the sides of the head main body so as not to protrude from the recesses, development of flaws in the screws formed from a magnesium alloy can be prevented effectively. In this case, thick portions are preferably formed in the sides of the metal head main body, to thus form the recesses in these thick portions. In addition, the recesses preferably protrude into the hollow section of the head main body from the exterior surface of the head main body.

According to the metal golf club head of the exemplary embodiment, preferable feeling of hitting and preferable hitting sound can be acquired.

An embodiment of the present invention will be described by reference to the drawings. However, the present invention is not limited to the embodiment provided below. FIG. 1A is a perspective view showing a head main body of a metal golf club head of an embodiment of the present invention; FIG. 1B is a cross-sectional view of the head main body taken along T1-T1 shown in FIG. 1A; FIG. 2A is a perspective view of the head main body when viewed from a direction differing from that where FIG. 1A is acquired; and FIG. 2B is a cross-sectional view of the head main body taken along T2-T2 shown in FIG. 2A.

A head main body 10 of the present embodiment has a sole 12, a crown 14, a toe-side 16, a heel-side 18, and a back-side 20. A hollow section 22 is formed in the head main body 10, and an opening section 23 closed by a face member is formed in a face side of the head main body 10. In the head main body 10 of the present embodiment, the toe-side 16 has a recess 24, and the heel-side section 18 is provided with a recess 26. The recesses 24 and 26 protrude from an exterior surface of the head main body 10 into the hollow section 22 of the head main body 10, and tip ends of the recesses are opened. Each of the recesses 24 and 26 has a large-diameter portion 28 on the exterior-surface-side of the head main body 10, and a small-diameter portion 30 is provided at an end of the large-diameter portion 28. A female thread 39 is formed along a circumferential surface of the small-diameter portion 30. In the drawing, reference numeral 38 designates a shaft insertion section.

A screw 32 formed from a magnesium alloy is screw-engaged with each of the recesses 24 and 26. As shown in FIG. 3, the screw 32 has a large-diameter portion 34 fitting to each of the large-diameter portions 28 of the recesses 24 and 26 and a small-diameter portion 36 fitting to each of the small-diameter portions 30 of the recesses 24 and 26. An external thread 37 is formed on a circumferential surface of the small-diameter portion 36. The smaller-diameter portions 36 are screw-engaged with the female threads 39 formed on the respective small-diameter portions 30 of the recesses 24 and 26, whereby the screws 32 are fastened to the head main body 10. In the present embodiment, slight clearance is formed between the internal circumferential surfaces of the large-diameter portions 28 of the recesses 24 and 26 and the outer circumferential surfaces of the large-diameter portions 34 of the screws 32.

In the present embodiment, an oxide film is formed on the surface of the screw 32 by means of anodizing, and epoxy-based coating is applied over the oxide film. The epoxy-based coating is also applied over the internal circumferential surfaces of the recesses 24 and 26. Moreover, an anaerobic adhesive 41 is filled into the clearance between the head main body 10 and the screws 32 (clearance between a step of the recess 24 and a step of the screw 32 and clearance between a step of the recess 26 and a step of the screw 32).

In the present embodiment, the screw is provided in the toe-side section and the heel-side section, respectively. However, a location where the screw of the present invention is to be provided is not limited to these positions. The screw can be provided, as appropriate, at one or two or more positions selected from the toe-side 16, the heel-side 18, and the back-side 20.

A head main body of a metal golf club head of the embodiment shown in FIGS. 1A to 2B is manufactured. In this case, the head main body is formed from a Ti-6Al-4V titanium alloy by means of investment casting. A face member is formed from a β-type titanium alloy by means of pressing. Screws are formed from a magnesium alloy (an AZ61 alloy). Each of the screws has an overall length of 15.5 mm; a large-diameter portion has a length of 10 mm and a diameter of 9.8 mm; and a small-diameter portion has a diameter of 5.75 mm and a mass of 1.5 g. A face member is fixed to the head main body by means of welding, and screws are fixed into two recesses of the head main body respectively, thereby completing a golf club head. In the metal golf club head of the present embodiment, a head volume is 460 cc; the least thickness of the crown is 0.6 mm; the least thickness of the sole is 0.9 mm; and the least thickness of the side sections is 0.7 mm. The face member is a thick face member having a thickness of 2.6 mm to 3.6 mm. The side where the recess is formed is made thick.

A golf club is manufactured by use of the metal golf club head. Feeling of hitting and hitting sound is evaluated by means of actual hitting of a golf ball by a golfer. Similar evaluation is also performed by use of a hollow iron golf club head (Comparative Example 1) where screws formed from nylon are fixed to the respective two recesses and a hollow iron golf club head (Comparative Example 2) where screws formed from stainless steel are fixed to the respective two recesses. The weight of the screw formed from a magnesium alloy is 1.5 g/piece; the weight of the screw formed from nylon is 0.9 g/piece; and the weight of the screw formed from stainless steel is 6.5 g/piece. Consequently, evaluation by the golfer is as follows.

Metal Golf Club Head of the Embodiment

Hitting sound between hitting sound generated by the club head using the screws formed from stainless steel and hitting sound generated by the club head using screws formed from nylon

Sound is not muffled, and a high-pitched sound is generated.

Only sound echoed.

Optimum feeling of a ball being repelled by a face

Metal Golf Club Head of Comparative Example 1

Sound is muffled.

Mild but insufficient feeling of hitting

Feeling of hitting is not transmitted well.

Sound did not echo, and less feeling of hitting is transmitted. No feeling of far flying of a ball is obtained.

Metal Golf Club Head of Comparative Example 2

Sound echoed, but the head felt hard

High-pitched sound

Feeling of a ball being repelled by a face and departing quickly

Difficulty seemed to be encountered in controllably hitting a ball

A relationship between the oscillation frequency of the head and an attenuation ratio is examined through modal analysis by use of the golf club head of the embodiment, the golf club head of Comparative Example 1, and the golf club head of Comparative Example 2. Modal analysis is an analytical technique which will be described below. Specifically, when force is exerted on a structure from the outside, the structure starts and keeps vibrating continually. The vibrations have a characteristic shape (a characteristic mode). Vibrations arise at a characteristic frequency (characteristic vibrations) and attenuate (a modal damping ratio). Modal analysis is an analytical technique for determining characteristic dynamic properties (modal parameters); namely, a characteristic mode, characteristic vibrations, and a mode damping ratio. In this test, vibration characteristics of the golf club heads are evaluated by means of modal analysis through use of an impact hammer. Results of the test are plotted in a graph of FIG. 4.

The golf club head of the embodiment using the screws formed from a magnesium alloy is understood to be higher, at low frequencies, in damping ratio than the golf club head of Comparative Example 2 using the screws formed from stainless steel. The golf club head of the embodiment is understood to be, at high frequencies of 5000 Hz or more, equal in damping ratio to the golf club head of Comparative Example 2 using the screws formed from stainless steel and to exhibit an appropriate vibration damping characteristic. In contrast, the golf club head of Comparative Example 1 using the screws formed from nylon is understood to be high in damping ratio at all frequencies and to exhibit an excessively-high vibration damping effect. The golf club head of Comparative Example 2 using the screws formed from stainless steel is understood to have a low damping ratio at all frequencies and to exhibit a low vibration damping effect. 

1. A metal golf club head comprising: a metal head main body; and an anticorrosion screw that is formed from a magnesium alloy and fastened to predetermined location on the metal head main body.
 2. The metal golf club head according to claim 1, wherein the anticorrosion screw is coated with an oxide film.
 3. The metal golf club head according to claim 1, wherein the anticorrosion screw is made by forming an external thread through machining and forming an oxide film on a surface of the external thread.
 4. The metal golf club head according to claim 1, wherein the anticorrosion screw is coated with paint.
 5. The metal golf club head according to claim 1, wherein a surface of the metal head main body is coated with paint after the anticorrosion screw is fastened to the predetermined location of the head main body.
 6. The metal golf club head according to claim 1, wherein the anticorrosion screw is fastened to a side of the metal head main body.
 7. The metal golf club head according to claim 1, wherein: a recess is formed in a side of the metal head main body; and the anticorrosion screw is fastened to inside of the recess so as not to protrude from the recess. 